The present invention relates to industrial processes for the production of diphenyl sulfone compounds represented by Formula (II) and useful as developers for leuco dyes to be used in thermal recording papers, and in more detail, to processes for the efficient production of the said diphenyl sulfone compounds by the recovery and reuse of harmful halogen compounds without discharging them into the environment.
Processes for the preparation of diphenyl sulfone compounds of Formula (II) are disclosed in Japanese Patents Laid-open Nos. Sho 58-20493, Sho 58-82788, Sho 60-13852 and Sho 60-56949, that 4,4xe2x80x2-dihydroxydiophenyl sulfone is reacted with a halogen compound, such as alkyl halide, in a polar solvent, such as dimethylformamide or alcohol, in the presence of an alkali. These processes have a drawback of difficulty to improve the selectivity of reactions because of the use of solvents that dissolve reaction reagents and products well. There was a problem that noticeable amounts of diether derivatives, i.e., 4,4xe2x80x2-disubstituted hydroxydiphenyl sulfones, are produced as byproducts.
WO 91/11433 has reported that a reaction of a mole of 4,4xe2x80x2-dihydroxydiphenyl sulfone with an alkyl halide in the presence of 1.5 to 3 moles of alkali in 0.3 to 1.5 parts by weight of an aqueous solvent to a part by weight of 4,4xe2x80x2-dihydroxydiphenyl sulfone results in satisfactory selectivity and yield. However, when alkyl chlorides are used, it takes a long time to complete the reaction because of their low reactivity. Besides, alkyl iodides are expensive. Therefore, alkyl halides able to use in industry are practically limited to alkyl bromides. The said WO patent reports only examples of using alkyl bromides.
If an alkylation is carried out using an alkyl bromide under the above reaction conditions, crystals are deposited as the reaction proceeds. The inside of the system becomes viscous and heterogeneous, resulting in insufficient stirring. Therefore, there is a problem of incompletion of the reaction.
Of compounds of Formula (II) useful as developers for leuco dyes to be used in thermal recording papers, compounds where R is isopropyl are produced using isopropyl bromide, which is hardly produced domestically. Therefore it is difficult to procure the starting material stably.
It is an object of the present invention to provide industrial processes for the production of diphenyl sulfone compounds of Formula (II) by using alkylating agents that are supplied stably, instead of alkyl bromide, with productivity, economical efficiency and safety.
The inventors of the present invention studied various alkylations, such as those with alkyl sulfates, by addition of unsaturated hydrocarbons, and of using alkyl chlorides or alkyl iodides. As a result, it was found that use of alkyl iodides and the like could greatly shorten production times, and that almost all of alkyl iodides and the like used in the reactions could be recovered as inorganic iodide salts. An iodine recovery step in which iodine is recovered from manufacturing waste water containing the salts and reacted with an alcohol to self-produce an alkyl iodide or the like, is incorporated in the production process. Then, iodine is completely recovered for reuse. The process is more improved in productivity and economic efficiency than those of the prior art. Thus, the present invention has been completed.
The present invention relates to (1) an industrial process for the production of diphenyl sulfone compounds of Formula (II) 
(wherein, R is straight or branched chain alkyl, straight or branched chain alkenyl, straight or branched chain alkynyl, or optionally substituted cycloalkyl), characterized in that 4,4xe2x80x2-dihydroxydiphenyl sulfone is reacted with a compound represented by Formula (I)
RI
(wherein, R is as defined above) in the presence of a base at reaction temperature of 70 to 110xc2x0 C., preferably 70 to 90xc2x0 C.
It relates to (2) an industrial process for the production of diphenyl sulfone compounds according to (1), in which 0.8 to 2 moles of a compound of Formula (I) and 2 to 4 moles of a base are used to a mole of 4,4xe2x80x2-dihydroxydiphenyl sulfone, and the concentration of the base is made 20 to 50% by weight with water used as a solvent.
It relates to (3) an industrial process for the production of diphenyl sulfone compounds according to (1) or (2), in which a reaction time is 4 to 15 hours.
It relates to (4) an industrial process for the production of diphenyl sulfone compounds according to one of (1) to (3), in which a compound of Formula (I) is where R is isopropyl.
It relates to (5) an industrial process for the production of diphenyl sulfone compounds represented by Formula (II) 
(wherein, R is as defined above), characterized by containing an iodine recovery step that 4,4xe2x80x2-dihydroxydiphenyl sulfone is reacted with a compound of Formula (I)
RI
(wherein, R is as defined above) in the presence of a base, iodine is recovered from iodides contained in waste water, and the recovered iodine is reacted with an alcohol corresponding to a compound of Formula (I) to be used for the reaction, to give a compound of Formula (I).
It relates to (6) a process for the production of diphenyl sulfone compounds according to (5), in which a step is further incorporated that iodine is recovered from waste water discharged when a compound of Formula (I) is produced by a reaction of the previously recovered iodine with an alcohol corresponding to the compound of Formula (I) to be used for the reaction, and reused for the production of compounds of Formula (I).
It relates to (7) an industrial process for the production of diphenyl sulfone compounds according to (5) or (6), in which 4,4xe2x80x2-dihydroxydiphenyl sulfone is reacted with a compound of Formula (I) in the presence of a base at 70 to 110xc2x0 C., preferably 70 to 90xc2x0 C.
It relates to (8) an industrial process for the production of diphenyl sulfone compounds according to one of (5) to (7), in which 0.8 to 2 moles of a compound of Formula (I) and 2 to 4 moles of a base are used to a mole of 4,4xe2x80x2-dihydroxydiphenyl sulfone, and the concentration of the base is made 20 to 50% by weight with water used as a solvent.
It relates to (9) an industrial process for the production of diphenyl sulfone compounds according to one of (5) to (8), in which a reaction time is 4 to 15 hours.
It relates to (10) an industrial process for the production of diphenyl sulfone compounds according to one of (5) to (9), in which a compound of Formula (I) is where R is isopropyl.
Examples of compounds of Formula (I) used in the methods of the present invention include alkyl iodides such as methyl iodide, ethyl iodide, n-propyl iodide, isopropyl iodide, n-butyl iodide, isobutyl iodide, sec-butyl iodide, pentyl iodide, hexyl iodide, heptyl iodide and octyl iodide; alkenyl iodides such as allyl iodide; and cycloalkyl iodides such as cyclohexyl iodide.
In the present invention, compounds of Formula (I) (hereinafter abbreviated as alkyl iodides and the like) are preferably used 0.8 to 2 equivalents, more preferably 1.0 to 1.6 equivalents, to 4,4xe2x80x2-dihydroxydiphenyl sulfone.
Generally, alkyl iodides and the like are more reactive than alkyl bromides and the like, so that selectivity is not good. For example, production rates of monoalkyl and dialkyl products of 4,4xe2x80x2-diphenyl sulfone are reduced. The inventors of the present invention, however, found out that, if water is used as a reaction solvent, selectivity is not deteriorated, because solubility of alkyl iodides and the like to water is lower than that of alkyl bromides and the like (for example, solubility of isopropyl bromide: 0.381 g/100 g of water; and isopropyl iodide: 0.139 g/100 g of water).
As describe above, solubility of alkyl bromides and the like to water is larger than that of alkyl iodides and the like. Thus, there is a problem that alkyl bromides and the like are susceptible to hydrolysis by bases that are not forming salts with 4,4xe2x80x2-dihydroxydiphenyl sulfone. Therefore, it is necessary to use considerably excessive amounts of alkyl bromides and the like and bases in order to increase reaction conversion rates. In the case of alkyl iodides and the like, which are less soluble in water and more reactive, reaction conversion rates can be improved to 95% from 70% of the prior art, by using only 1.5 equivalents.
The present invention is characterized by a reaction using an alky iodide or the like in the presence of a base in a reaction temperature range between 70 and 110xc2x0 C., preferably 70 and 90xc2x0 C.
Alkyl iodides and the like are more reactive and have higher boiling points than alkyl bromides and the like, so that reaction temperatures can be raised at ordinary pressure without using special apparatuses. Therefore, reaction efficiency is improved and reactions are completed in shorter times than when alkyl bromides and the like are used. For example, the reaction is completed in about 8 hours when it is carried out using 1.07 equivalents of isopropyl iodide to 4,4xe2x80x2-dihydroxydiphenyl sulfone at 70xc2x0 C. However, the same reaction but using isopropyl bromide does not finish completely in even twice a longer time of 16 hours. An alkylation using isopropyl iodide at a reaction temperature of 90xc2x0 C. finishes in about 4 hours. Compared to it, it is impossible to carry out a reaction with isopropyl bromide at a reaction temperature of 90xc2x0 C. except using a special apparatus. Reactions using isopropyl iodide can be carried out at temperatures above the boiling points of alkyl iodides and the like, if special apparatuses are used for reactions under pressure and other cases. Reaction efficiency is improved in terms of the shortening of reaction times and the like. This is however not preferable for industrial use.
Examples of bases used as acid removing agents include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide; or alkali metal carbonates such as sodium carbonate and potassium carbonate. Alkali metal hydroxides are particularly preferred.
An amount of a base used gives great influence on reaction selectivity, together with an amount of water used as a reaction solvent: It is favorable to use 2 to 4 moles, preferably 2.2 to 3.2 moles, of a base to a mole of 4,4xe2x80x2-dihydroxydiphenyl sulfone, and an amount of water to make a base concentration 20 to 50% by weight, preferably 30 to 35% by weight in order to improve reaction selectivity. Di-alkali salts of 4,4xe2x80x2-dihydroxydiphenyl sulfones are highly soluble in water, but mono-alkali salts of 4,4xe2x80x2-dihydroxydiphenyl sulfones are less soluble in water. Therefore, as reactions proceed, mono-substituted metal salts of products are deposited so that the mono-substituted products are obtained selectively. Because of this, it is favorable to use 2 equivalents or more of a base to 4,4xe2x80x2-dihydroxydiphenyl sulfone at the beginning of the reaction, and, when hot, an amount of water to make a base concentration 20% by weight or more and to dissolve di-alkali salts only. If the alkali concentration is less than 20% by weight, selectivity is lowered because the mono-alkali salts of products are dissolved. On the other hand, the viscosity of the reaction solution rises in the case of 50% by weight or more, with a problem of facilities.
According to the methods of the present invention, iodine of alkyl iodides and the like used is almost all recovered as salts after the reaction. It becomes possible to recover iodine from waste water containing the salts.
The iodine recovery step consists of recovery of iodine from iodides contained in waste water discharged when a diphenyl sulfone compound of Formula (II) is produced, and production of an alkyl iodide or the like by a reaction of the recovered iodine with an alcohol corresponding to an alkyl iodide or the like to use for the reaction. Furthermore, it is favorable to contain a step of further recovering iodine from waste water when the alkyl iodide or the like is produced and reusing it for the production of an alkyl iodide.
Examples of steps of recovering iodine are described in the following: First, 4,4xe2x80x2-dihydroxydiphenyl sulfone is alkylated with an alkyl iodide in the presence of a base; a small amount of di-alkyl byproducts produced is separated by filtration after the completion of the reaction; the filtrate is adjusted pH with an acid; an organic solvent that dissolves the target compound, such as toluene, is added; and the resulting solution is separated to an organic layer containing the target compound and an aqueous layer containing a sodium salt of unreacted 4,4xe2x80x2-dihydroxydiphenyl sulfone and iodides of the base.
Then, the pH of the aqueous layer is adjusted to recover unreacted 4,4xe2x80x2-dihydroxydiphenyl sulfone. There are no particular restrictions on a range of pH adjustment, if on the acidic side. It is however preferable to be in the range between pH 0.5 and 4.0, particularly pH 2.0 and 3.0, in consideration of the following iodine recovery step. There are no particular restrictions on acids used. Preferred include mineral acids such as hydrochloric acid and sulfuric acid. After most organic components are removed as described above, iodine is liberated from the aqueous layer. Examples of methods of liberation include oxidation with oxidizing agents and direct electrolysis. The oxidation with oxidizing agents is preferred from the viewpoint of equipment and cost.
Examples of oxidizing agents used include chlorine, hypochlorous acid or its salt, hydrogen peroxide, or oxygen. Chlorine is particularly preferred when taking into consideration treatments of waste water and cost. A desirable amount of an oxidizing agent used is 1 to 1.5 times, preferably 1.0 to 1.3 times, that of iodine in molar ratio. It is desirable, prior to addition of the oxidizing agent, to add an acid, such as hydrochloric acid or sulfuric acid, to adjust the solution to pH 0.5 to 3.0, preferably 1.0 to 2.0.
Methods known in the art to collect iodine from the water containing the liberated iodine include those using blow-out, ion exchange resins, copper, activated carbon or pressure melting. Any of them can be applied. The pressure melting method is preferred by taking into consideration the fact that in the reactions, most organic compounds and impurities are removed at the intermediate step and that iodine of high quality is obtained using relatively simple equipment.
In more detail, for example, the liberated iodine is separated from water by a cyclone-type centrifugal separator, then heated to 130 to 150xc2x0 C. under pressure for melting, and cooled to solidify for making flakes, sublimed crystals or blocks, or powder or granules. To obtain spherical iodine, which is less sublime and easily handled, it is preferable to flow out the melt from a fine jetting nozzle in diameter at a constant speed, and to cool it to solidify by cooling gas in the midway of falling.
Known methods of preparing alkyl iodides and the like with iodine include a method of using hydrogen, iodine and methanol as starting materials in the presence of a rhodium, iridium or ruthenium catalyst; a reaction of a metal of Ia, IIa, IIIa, Ib, IIb or IVb Group in Periodic Table, iodine and an alcohol or the like at 15 to 150xc2x0 C. and 1 to 50 atm; and a method of using an alcohol, iodine and red phosphorus. It is preferable to use the method of using red phosphorus when taking into consideration reaction equipment and cost.
In more detail, for example, an alkyl iodide can be synthesized by that red phosphorus is suspended in an alcohol, iodine is dropped while heating, and the product is distilled from the reaction solution. In an industrial scale, an alkyl iodide may be prepared in a way that red phosphorus suspended in an alcohol is dropped into an alcohol solution of iodine. Either anhydrous red phosphorus or red phosphorus containing water can be used. The latter is preferred because of safety. Red phosphorus containing 10 to 40 mol %, preferably 10 to 30 mol %, of water to phosphorus is used.
A reaction solvent is usually an alcohol that becomes a reaction substrate. It is possible to mix with water. It is preferable to carry out the reaction in the coexistence of water, particularly for the purpose of preventing the reaction from becoming out of control. An amount of water used is in the range of 5 to 20 ml/atom mol, preferably 10 to 15 ml/atom mol, based on an amount of iodine used. If it is less than 5 ml/atom mol, there is no effect. If more than 20 ml/atom mol is used, the reaction is checked. There are no particular restrictions on amounts of water used to suspend red phosphorus, if red phosphorus is sufficiently suspended in water within the range of giving no impediment of dropping. Water of roughly equal weight to that of red phosphorus is usually sufficient.
In this reaction, iodine (I2), phosphorus and an alcohol react at a molar ratio of 3:2:6. It is however preferable to use 1 to 1.5 moles of alcohol and 0.2 to 0.3 moles of red phosphorus, to 1 atom mol of iodine, when taking into consideration reaction efficiency and iodine that is present in waste water and is used again in the recovery step.
The reaction is carried out by a method of adding iodine to an alcohol and red phosphorus, or adding phosphorus to an alcohol and iodine, at temperature of about the boiling point of the alcohol. The reaction exothermally proceeds simultaneously with the addition. Therefore, it becomes difficult to control the reaction if an addition rate is too fast. It is necessary to keep an appropriate reaction rate.
The target alkyl iodide or the like can be isolated from the reaction solution by distillation after the completion of the reaction. It can also be isolated by steam distillation. Particularly when iodine is further recovered from the residue in the vessel after the distillation, it is advantageous if contained phosphorus-iodine compounds and the like are sufficiently hydrolyzed. Steam distillation is preferred when the recovery step is taken into account.
4,4xe2x80x2-Dihydroxydiphenyl sulfone to be recovered in a post-treatment step, the alcohol produced from the reaction and recovered, and the re-produced alkyl iodide or the like are used again as part or the whole of starting materials for the reaction. They can be reused with no problems of reaction yields and the quality of products. Products with nearly equal quality can be prepared when compounds of Formula (II) are synthesized with alkyl bromides, or with alkyl iodides and the like and a recovery step included. The latter is more advantageous in terms of cost and productivity. It has become possible to use alkyl iodides and the like as alternative materials to alkyl bromides and the like.
The present invention is described in more detail in reference to Examples, but is not limited to the examples.